Advantages have been achieved in Field Effect Transistors using the physical properties of compound semiconductors. The use of a heterojunction between two compound semiconductors in the channel of a FET employed to enhance carrier mobility in that channel is shown in U.S. Pat. No. 4,538,165, and the use of a higher bandgap semiconductor as the gate in an FET is shown in U.S. Pat. No. 4,379,005.